by Susan Davis, USA TODAY

by Susan Davis, USA TODAY

WASHINGTON - President Obama prepared for the possibility of launching a U.S. military action against Syria within days, even as Britain Thursday opted out in a vote by Parliament.

Advisers said the president would be willing to retaliate against Syria alone.

"The president of the United States is elected with the duty to protect the national security interests in the United States of America," White House spokesman Josh Earnest said.

Caitlin Hayden, National Security Council spokeswoman, said the United States would continue to consult with Britain but Obama would make decisions based on "the best interests of the United States."

"As we've said, President Obama's decision making will be guided by what is in the best interests of the United States," Hayden said. "He believes that there are core interests at stake for the United States. He believes that there are core interests at stake for the United States and that countries who violate international norms regarding chemical weapons need to be held accountable."

U.S. Rep. Eliot Engel, D-N.Y., top Democrat on the House Foreign Affairs Committee, said after a White House teleconference with some Congress members Thursday, "The main thing was that they have no doubt that (Syrian President Bashar) Assad's forces used chemical weapons."

He said administration officials did not provide new evidence but revealed the government has intercepted "some discussions and some indications from a high-level official" in Syria regarding use of gas.

U.S. Sen. Bob Corker, R-Tenn., ranking member of the Senate Foreign Relations Committee, said he would support "surgical, proportional military strikes" given the evidence of continued use of chemical warfare.

"Whatever limited action is taken should not further commit the U.S. in Syria beyond the current strategy to strengthen the vetted, moderate opposition," he said. "While the administration has engaged in congressional consultation, they should continue to be forthcoming with information and would be far better off if they seek authorization based upon our national interests, which would provide the kind of public debate and legitimacy that can only come from Congress."

A White House statement released after the 90-minute teleconference said the call included, among others, National Security Adviser Susan Rice, Secretary of State John Kerry, Secretary of Defense Chuck Hagel and 26 lawmakers - the chairs and ranking members of national security committees within Congress.

"The views of Congress are important to the President's decision-making process, and we will continue to engage with Members as the President reaches a decision on the appropriate U.S. response to the Syrian government's violation of international norms against the use of chemical weapons," the White House statement read.

Earlier, the White House stepped up efforts to consult with Congress in advance of any U.S. military intervention in Syria, including private communications between President Obama and House Speaker John Boehner, R-Ohio, and a conference call for congressional leaders with senior administration officials.

"That conference call is just the latest in a series of robust congressional consultations that everybody from the president on down in the administration have been engaged in over the last few days," Earnest said of the Thursday evening briefing.

More than one quarter of the 435-member House has signed a letter authored by Rep. Scott Rigell, R-Va., calling on the president to seek a formal vote for congressional authorization for action in Syria. Boehner has stopped short of calling for a vote, but has publicly chided the president for not making a strong enough case to either Congress or the public.

Following a private call with the president on Thursday, Brendan Buck, a spokesman for Boehner said "it is clear that further dialogue and consultation with Congress, as well as communication with the American public, will be needed."

The White House is unlikely to seek formal congressional approval, but Earnest said the White House is making an effort to consult closely with Congress.

Defense Secretary Chuck Hagel said Friday the Obama administration was consulting with allies to "further develop the facts" about last week's alleged chemical weapons attack in Syria, and options for a response.